1. Field of the Invention
The present invention relates, generally, to a dye-sensitized solar cell comprising an ion-bound oligomer complex. More particularly, the present invention relates to a dye-sensitized solar cell comprising an ion-bound oligomer complex electrolyte, which comprises a first oligomer having a C5-30 heteroaryl group containing a nitrogen heteroatom as a basic functional group at both ends of the molecule, mixed with a second oligomer having an acidic functional group at both ends of the molecule. The acidic group can be selected from among carboxylic acid, phosphoric acid, and sulfonic acid, at both ends of the molecule, to thus form a salt. The solar cell exhibits the desired mechanical properties, can be manufactured conveniently, and can have a high energy conversion efficiency. Also provided is a method for manufacturing a dye-sensitized solar cell comprising an ion-bound oligomer complex.
2. Description of the Related Art
In general, a solar cell is a photovoltaic device used for the conversion of solar light into electrical energy. A solar cell is usable without limitation, is environmentally friendly, unlike other energy sources, and, is thus expected to become an increasingly important energy source over time. In particular, it is expected that solar cells can be electrically charged solely using solar light and as such, can be mounted to various portable information instruments, such as portable computers, mobile phones, personal portable terminals, and the like.
Conventionally, silicon solar cells made of monocrystal or polycrystal silicon have been mainly utilized. However, the silicon solar cell suffers from disadvantages because it requires the use of large and expensive equipment and subsequently has a high manufacturing cost. Further, the ability to increase the conversion efficiency of solar energy into electrical energy is limited. Therefore, there is a need for novel alternatives.
An alternative to the silicon solar cell, is a solar cell comprised of organic material which can be inexpensively manufactured. In particular, a dye-sensitized solar cell having a very low manufacturing cost is considered. The dye-sensitized solar cell is a photoelectrochemical solar cell comprising a photoelectrode composed of metal oxide nanoparticles having dye particles adsorbed thereon, a counter electrode, and a redox electrolyte loaded in the space between the two electrodes. The photoelectrode consists of a conductive transparent substrate, a metal oxide layer comprising metal oxide, and a dye.
When solar light is incident on the solar cell, photons are first absorbed by the dye. When the dye absorbs solar light it is transformed into an excited state, such that the electrons are transferred to the conduction band of metal oxide and the holes are transferred to the electrolyte layer. The electrons are transferred to the electrode and then flow to the external circuit in order to transmit electrical energy, after which they are transferred to the counter electrode in a lower energy state, at which point the transmitted energy is depleted.
Although a conventional dye-sensitized solar cell using a liquid electrolyte has high energy conversion efficiency, its properties deteriorate over time due to leakage of the electrolyte and evaporation of the solvent. This instability has been related to the detection of salts at low temperatures, and to the use of an organic solvent. Consequently, this type of solar cell is difficult to commercialize. Various attempts have been made to prevent the leakage of the electrolyte. In particular, a dye-sensitized solar cell has been developed using a solid electrolyte that is able to increase the stability and the durability of the solar cell.
Further, in response to the above-mentioned problems with the liquid electrolyte, a gel-type electrolyte has been proposed which enables the electrolyte to penetrate into a polymer. However, this solution is problematic because the viscosity of the gel-type electrolyte is high, and because the gel-type electrolyte is crosslinked by weak interactions between the polymers and thus is easily liquefied when heated.
In this regard, there has been proposed a dye-sensitized solar cell including poly(vinylenefluoride-co-hexafluoropropylene) dissolved in a solvent, such as N-methyl-2-pyrrolidone or 3-methoxypropionitrile, which has a high boiling point. Although the polymer electrolyte thus prepared has high ionic conductivity, similar to the liquid electrolyte at room temperature, it has poor mechanical properties which make it difficult to manufacture the solar cell. In addition, the water-retaining property of the polymer electrolyte is decreased (M. G. Kang et al., ECS., 151, E257, 2004).
In the case of the solar cell using a solid electrolyte, in order to mitigate the problems of low energy conversion efficiency due to the solvent, the solvent is removed from the prepared electrolyte solution. As a result, the electrons received by the photoelectrode are easily reduced using a hole conductive material, which is also in a solid phase to oxidize the dye again resulting in current flow.
Moreover, with the goal of increasing the energy conversion efficiency of the dye-sensitized solar cell using a solid electrolyte, it is also important to develop a polymer electrolyte having high ionic conductivity in order to prevent or inhibit electron recombination. Accordingly, the development of such solar cells is still required.